It is known to embed anchors in steel reinforced concrete structures. For example, anchors may be embedded in precast sections for a variety of purposes, which range all of the way from hanging utilities such as piping, to hanging facade, or even lifting the precast section. In poured-in-place steel reinforced concrete structures, rods which are bent or hooked, and which may have a protruding threaded end are often employed. Some include an exposed threaded or grout socket. Some hanging systems form holes in the concrete and then drive or wedge in fasteners. Some grout or literally glue (epoxy) a fastener or bracket in the hole. Nails or other studs can be driven in concrete with enough impact.
Recent code changes have significantly increased the amount of steel reinforcing used in concrete structures, while designers are striving for thinner or more compact structural elements. The result is more steel reinforcing congestion and placement problems. This is one of the reasons that headed anchors are preferred since they eliminate the need for substantial lengths of bent or hooked reinforcing bar, thus minimizing steel congestion. Headed anchors are also less unwieldy, that is they are smaller and more compact and are easier to install at the site.
Most of the above fastening systems bear little, if any, compatible relationship to the steel reinforcing of the poured-in-place or precast concrete. While some may hook over a reinforcing bar or even be threaded to a bar end, the fasteners or anchors employed are not readily adaptable to concrete sections with spaced layers of steel reinforcing.
Where multiple layers or mats of reinforcing are provided, the enlarged head of any anchor for a hanger should literally be behind both layers. By "behind" is meant on the opposite side of the load. For example, if a heavy pipe is hung from a slab or deck, the head of the anchor should be above the uppermost layer of steel reinforcing. If a vertical exterior panel or cladding is hung from a steel reinforced concrete frame, the head of the anchor should be behind the innermost layer of steel reinforcing. In fact, some codes now require this placement of the anchor head. Complicating the matter further is that the head should also be spaced from the top of the slab or deck, or the interior of the frame. With such positioning, the shear cone for a round head (pyramid for a rectangular head) has an enlarged base on the surface from which the load is supported and the reinforcing extends through the cone or pyramid zone as shear connectors.
While some structures are sufficiently large that anchors or hangers may be customed designed for the project, the tolerances in steel reinforcing for large structures are such that even customed designed anchors seldom fit easily. In most structures, there will be substantial variation in dimensions, some of which is intended. For example, as a building rises, columns and other main frame elements usually get smaller. Spans and slab or deck thickness may vary. Even a custom anchor actually may have a number of size variations. Accordingly, it would be desirable to have an adjustable or dimension variable headed anchor which could properly be positioned with respect to the steel reinforcing and the structure surfaces, regardless of the thickness or dimension variations.
Another problem with anchors is corrosion. Anchors exposed to chloride intrusions or a corrosive environment will rust or corrode if not properly protected. A hanger, rod or other part of the hanging system outside the concrete structure can be inspected, coated, recoated and, if necessary, fairly inexpensively replaced. That, however, is not true for the part of the anchor or hanging system embedded in concrete.
The corrosion of steel in concrete causes the concrete to spall and crumble. Repair or replacement is an expensive undertaking. Accordingly, it would be desirable that the ultimate anchor head have minimal exposure to the environment and any part exposed be capable of being thoroughly coated or sealed.